Active stylus differential synchronization

ABSTRACT

A touch-sensing system is disclosed. The system includes a display device including a touch sensor having a plurality of electrodes, and drive logic coupled to the plurality of electrodes and configured to drive the plurality of electrodes during a plurality of touch-sensing frames, each of which includes a stylus sync sub-frame during which the drive logic drives at least some of the plurality of electrodes, referred to for that stylus sync sub-frame as sync-driven electrodes, with synchronization waveforms that are communicated electrostatically to cause synchronization of the display device with an active stylus. For each of the stylus sync sub-frames, the drive logic may be configured to differentially drive the sync-driven electrodes of such stylus sync sub-frame, such that a first synchronization waveform used to drive one of the sync-driven electrodes is different than a second synchronization waveform used to drive another of the sync-driven electrodes.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/453,869, filed Feb. 2, 2017, the entirety of which is herebyincorporated herein by reference.

BACKGROUND

Some touch sensors are configured to detect touch input by sensingchanges in capacitance at electrode locations in an electrode matrix.Touch inputs may be from a user's body (e.g., a finger) and, in somecases, a passive or active stylus. In active-stylus implementations, thestylus may be synchronized with the touch sensor to achieve a sharedsense of time between the stylus and touch sensor. This may, among otherthings, facilitate determinations of stylus position relative to thetouch sensor.

Multiple electrodes of the matrix may be driven simultaneously with asynchronization waveform. Via capacitive coupling, this causes currentto flow into a tip electrode of the stylus. The current pattern isprocessed in receive logic of the stylus to achieve synchronization.Current flowing into the stylus tip may be affected by variouscapacitances and other conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example display device including a touch sensorreceiving touch inputs from a user's body and an active stylus.

FIG. 2 shows a cross-sectional view of an optical stack of the displaydevice of FIG. 1.

FIG. 3 shows an example touch sensor matrix and active stylus.

FIG. 4 shows an example touch-sensing frame, including a stylus syncsub-frame during which the active stylus and display device of FIGS. 1and 3 may communicate electrostatically to synchronize the displaydevice and stylus.

FIG. 5 shows different sets of sync-driven row electrodes that may bedifferentially driven in different stylus sync sub-frames to facilitatesynchronization.

FIG. 6 shows an example touch-sensing method.

FIG. 7 shows an example touch-sensitive display device.

FIG. 8 shows an example in-cell touch sensor matrix.

FIG. 9 shows an example touch-sensing frame of the in-cell touch sensormatrix of FIG. 8.

FIG. 10 shows an example sensel grouping.

FIG. 11 shows another example sensel grouping.

FIG. 12 shows another example-touch sensing method.

FIG. 13 shows a block diagram of an example computing device.

DETAILED DESCRIPTION

Some touch sensors are configured to detect touch input by sensingchanges in capacitance in an electrode matrix. As used herein, “matrix”refers to, among other things, intersections between elongate row andcolumn electrodes at which mutual capacitance is measured by driving atone, and receiving at the other, of the row and column electrodes. Inother examples, “matrix” also refers to an array of locations where theself-capacitance of electrodes is measured, with both driving andreceiving occurring at the electrodes. Indeed, “matrix” is applicable toany electrode scheme in which capacitance measurements are localized toXY coordinates across a touch-sensitive display or other expanse. In theexamples herein, touch inputs may be detected from contact and/or hoverof a user's body (e.g., a finger) and an active stylus over theelectrode matrix. The stylus may be synchronized with the touch sensorto achieve a shared sense of time between the stylus and touch sensor(and/or a display device incorporating the touch sensor). Among otherthings, the shared sense of time facilitates determinations of relativestylus position.

Synchronization typically is performed every touch-sensing frame duringa sub-frame referred to as a stylus sync sub-frame. During a stylus syncsub-frame, electrodes are driven with synchronization waveforms. For agiven stylus sync sub-frame, the activated electrodes are referred to assync-driven electrodes. Via capacitive coupling of sync-drivenelectrodes with a tip electrode in the active stylus, synchronizationsignals are received into receive logic of the stylus, in the form ofcurrent patterns flowing into the stylus tip (e.g., time varying currentwaveform). The inbound current pattern is processed in the receive logicto perform synchronization. In the examples herein, electrodes spanningthe matrix (e.g., a subset of electrodes) are activated as sync-drivenelectrodes, allowing the stylus to achieve synchronization regardless ofits vertical coordinate relative to the electrodes.

Current flowing into the stylus tip may be affected by variouscapacitances and other conditions. One challenge in particular may occurwhen the user's body comes into contact with the matrix. Even when suchcontact is relatively small (e.g., a fingertip as opposed to a restingpalm), the contact patch will typically result in a relatively largeincrease in capacitance between the user's body and activatedsync-driven electrodes. For example, as compared to the relatively smallstylus tip, the user's body may overlap a greater number of sync-drivenelectrodes, and/or over a greater portion of the overlapped electrodes.Accordingly, the increase in body-to-matrix capacitance resulting frombody contact may be significantly larger than the increase instylus-to-matrix capacitance resulting from stylus tip contact. This mayproduce a change at various voltage nodes to cause a current flow intothe user's body of sufficient magnitude to undesirably degrade currentflow into the stylus tip, thereby reducing synchronization performance.

Accordingly, the disclosure contemplates differential driving ofsync-driven electrodes within stylus sync sub-frames. Specifically, atleast some different synchronization waveforms are used for differentsync-driven electrodes. One sync-driven electrode might be driven withone waveform, while another, different synchronization waveform is usedfor another sync-driven electrode. In some cases, two waveforms may beused (e.g., two waveforms of inverse polarity) to drive sync-drivenelectrodes. In other cases, three or more different waveforms may beused. In some examples, two-value pulse trains are employed (e.g.,binary waveforms). In other cases, employed waveforms may includedigital waveforms taking on a greater range of values, analog waveforms,or any other type of waveforms.

Differential waveforms may be employed to provide cancellation to reducecurrent into a user's body. For example, within a given spatial groupingof sync-driven electrodes, differential waveforms may be employed so asto produce at least partially cancelling electrical conditions.Therefore, for a user body contact patch over that spatial grouping,current flowing into the user's body is reduced relative to what wouldoccur with undifferentiated driving (using the same waveform on all ofthe sync-driven row electrodes in the grouping).

In some examples, different sets of sync-driven electrodes may beemployed for different stylus sync sub-frames, with differentsynchronization waveforms being used in each set. In other words, oneset of sync-driven electrodes might be employed for one sub-frame, witha second, different set of sync-driven electrodes employed for the nextsub-frame. Any number of sets may be employed. Typically, the setsdiffer in that one or more electrodes function as sync-driven electrodesin one set, but not in another set. Reasons for omitting some electrodesfrom being activated during a sync sub-frame will be explained in detailbelow. For a given stylus contact point, shifting synchronizationwaveforms via use of different sets from frame-to-frame changes thedistance between those waveforms and the stylus contact point, whichaffects the signals received into the stylus. One of the sets may bepreferred for a given contact point, in that it brings a useful waveformclose to the stylus, while having potentially canceling waveformsfurther away from the stylus. In such a setting, position information ofthe stylus may be used to select a particular set for an upcoming syncsub-frame (i.e., selecting a set which results in a desired waveformbeing positioned as close as possible to the current stylus location).

Approaches to differentially driving electrodes in a touch sensor aredisclosed herein for both sensors that employ mutual capacitance sensingin a row/column electrode matrix, and for sensors that employself-capacitance sensing in an electrode matrix. In particular, FIGS.2-6 depict examples that relate to mutual capacitance sensing, whereasFIGS. 8-10 depict examples that relate to self-capacitance sensing. Itwill be understood that at least some of the approaches to differentialelectrode driving described with reference to mutual capacitance sensingmay be employed in connection with self-capacitance sensing, and that atleast some of the approaches to differential electrode driving describedwith reference to self-capacitance sensing may be employed in connectionwith mutual capacitance sensing, where adjustment may be potentiallymade when translating a differential driving method from one sensor typeto another.

FIG. 1 shows a touch interactive display system 100 including a displaydevice 102 that has a touch sensor 104. In some examples, display device102 may be a large format display with a diagonal dimension D greaterthan 1 meter, though the display may assume any suitable size. Displaydevice 102 may be configured to sense one or more sources of input, suchas touch input imparted via a digit 106 of a user and/or input suppliedby an input device 108, shown in FIG. 1 as a stylus. Digit 106 and inputdevice 108 are provided as non-limiting examples and any other suitablesource of input may be used in connection with display device 102.Display device 102 may be configured to receive input from styluses anddigits in contact with the display and/or “hovering” over the displaysurface. “Touch input” as used herein refers to both digit and non-digit(e.g., stylus) input, and to input supplied by input devices both incontact with, and spaced away from but proximate to, display device 102.In some examples, display device 102 may be configured to receive inputfrom two or more sources simultaneously, in which case the display maybe referred to as a multi-touch display.

Display device 102 may be operatively coupled to an image source 110,which may be, for example, a computing device external to, or housedwithin, the display. Image source 110 may receive input from displaydevice 102, process the input, and in response generate appropriategraphical output 112 for the display. In this way, display device 102may provide a natural paradigm for interacting with a computing devicethat can respond appropriately to touch input. Details regarding anexample computing device are described below with reference to FIG. 13.

FIG. 2 is a cross-sectional view of an optical stack 200 of displaydevice 102 (FIG. 1). Optical stack 200 includes a plurality ofcomponents configured to enable the reception of touch input and thegeneration of graphical output. As shown in FIG. 2, optical stack 200may include an optically clear touch sheet 202 having a top surface 204for receiving touch input, and an optically clear adhesive (OCA) 206bonding a bottom surface of the touch sheet to a top surface of a touchsensor 208, which may be touch sensor 104 (FIG. 1), for example. Touchsheet 202 may be comprised of any suitable materials, such as glass orplastic. As used herein, “optically clear adhesive” refers to a class ofadhesives that transmit substantially all (e.g., about 99%) of incidentvisible light.

As described in further detail below with reference to FIG. 3, touchsensor 208 includes a matrix of electrodes that form capacitors whosecapacitances may be evaluated in detecting touch input. As shown in FIG.2, the electrodes may be formed in two separate layers: a receiveelectrode layer (Rx) 210 and a transmit electrode layer (Tx) 212positioned below the receive electrode layer. Receive and transmitelectrode layers 210 and 212 may each be formed on a respectivedielectric substrate comprising materials including but not limited toglass, polyethylene terephthalate (PET), or cyclic olefin polymer (COP)film. Receive and transmit electrode layers 210 and 212 may be bondedtogether by a second optically clear adhesive 211. OCA 211 may be anacrylic pressure-sensitive adhesive film, for example. The touch sensorconfiguration illustrated in FIG. 2 is provided as an example;alternative arrangements are within the scope of this disclosure. Inother implementations, for example, layers 210, 211, and 212 may beintegrally formed as a single layer with electrodes disposed on oppositesurfaces of the integral layer. Further, touch sensor 208 mayalternatively be configured such that transmit electrode layer 212 isprovided above, and bonded to via OCA 211, with receive electrode layer210 being positioned therebelow.

Receive and transmit electrode layers 210 and 212 may be formed by avariety of suitable processes. Such processes may include deposition ofmetallic wires onto the surface of an adhesive, dielectric substrate;patterned deposition of a material that selectively catalyzes thesubsequent deposition of a metal film (e.g., via plating); photoetching;patterned deposition of a conductive ink (e.g., via inkjet, offset,relief, or intaglio printing); filling grooves in a dielectric substratewith conductive ink; selective optical exposure (e.g., through a mask orvia laser writing) of an electrically conductive photoresist followed bychemical development to remove unexposed photoresist; and selectiveoptical exposure of a silver halide emulsion followed by chemicaldevelopment of the latent image to metallic silver, in turn followed bychemical fixing. In one example, metalized sensor films may be disposedon a user-facing side of a substrate, with the metal facing away fromthe user or alternatively facing toward the user with a protective sheet(e.g., comprised of PET) between the user and metal. Althoughtransparent conducting oxide (TCO) is typically not used in theelectrodes, partial use of TCO to form a portion of the electrodes withother portions being formed of metal is possible. In one example, theelectrodes may be thin metal of substantially constant cross section,and may be sized such that they may not be optically resolved and maythus be unobtrusive as seen from a perspective of a user. Suitablematerials from which electrodes may be formed include various suitablemetals (e.g., aluminum, copper, nickel, silver, gold), metallic alloys,conductive allotropes of carbon (e.g., graphite, fullerenes, amorphouscarbon), conductive polymers, and conductive inks (e.g., made conductivevia the addition of metal or carbon particles).

Continuing with FIG. 2, touch sensor 208 may be bonded, at a bottomsurface of transmit electrode layer 212, to a display stack 214 via athird optically clear adhesive 216. Display stack 214 may be a liquidcrystal display (LCD) stack, organic light-emitting diode (OLED) stack,or plasma display panel (PDP), for example. Display stack 214 isconfigured to emit light L through a top surface of the display stack,such that emitted light travels in a light emitting direction throughlayers 216, 212, 211, 210, 206, touch sheet 202, and out through topsurface 204. In this way, emitted light may appear to a user as an imagedisplayed on top surface 204 of touch sheet 202.

Further variations to optical stack 200 are possible. For example,implementations are possible in which layers 211 and/or 216 are omitted.In this example, touch sensor 208 may be air-gapped and opticallyuncoupled to display stack 214. Further, layers 210 and 212 may belaminated on top surface 204. Still further, layer 210 may be disposedon top surface 204 while layer 212 may be disposed opposite and belowtop surface 204.

FIG. 2 also shows a controller 218 operatively coupled to receiveelectrode layer 210, transmit electrode layer 212, and display stack214. Controller 218 is configured to drive transmit electrodes intransmit electrode layer 212, receive signals resulting from driventransmit electrodes via receive electrodes in receive electrode layer210, and locate, if detected, touch input imparted to optical stack 200.Controller 218 may further drive display stack 214 to enable graphicaloutput responsive to touch input. Two or more controllers mayalternatively be provided, and in some examples, respective controllersfor each of receive electrode layer 210, transmit electrode layer 212,and display stack 214. In some implementations, controller 218 may beimplemented in image source 110 (FIG. 1).

FIG. 3 shows an example touch sensor matrix 300. Matrix 300 may beincluded in touch sensor 208 of optical stack 200 (FIG. 2) to bestowtouch sensing functionality to display device 102 (FIG. 1), for example.Matrix 300 includes a plurality of row electrodes and column electrodes.In the present example, the electrodes are shown in the form of rowelectrodes 302 vertically separated from column electrodes 304. Asdescribed below, the row electrodes may be transmitters/drivers, withvoltage waveforms (also referred to as “excitation waveforms”) beingused to stimulate them via operation of drive logic. This in turnaffects electrical conditions on the column electrodes (e.g., theexcitation waveform produces a time-varying current on the columnelectrode), and the column electrodes operate in a receive mode withaccompanying circuitry to process the induced electrical conditions.Referring again to FIG. 2, row electrodes 302 and column electrodes 304may be respectively formed in transmit electrode layer 212 and receiveelectrode layer 210 of optical stack 200, for example. Each intersectionof row electrodes 302 with column electrodes 304 forms a correspondingnode whose electrical properties (e.g., capacitance) may be measured todetect touch input. Three row electrodes 302 and three column electrodes304 are shown in FIG. 3 for the purpose of clarity, though matrix 300may include any suitable number of row electrodes and column electrodes,which may be on the order of one hundred or one thousand, for example.Any suitable number of electrodes may be employed, depending on thesetting.

While a rectangular grid arrangement is shown in FIG. 3, matrix 300 mayassume other geometric arrangements—for example, the matrix may bearranged in a diamond pattern. Alternatively or additionally, individualelectrodes in matrix 300 may assume nonlinear geometries—e.g.,electrodes may exhibit curved or zigzag geometries, which may minimizethe perceptibility of display artifacts (e.g., aliasing, moiré patterns)caused by occlusion of an underlying display by the electrodes. Inaddition, “row” and “column,” as used herein, does not imply anyparticular orientation relative to the display or to the floor/ground.In other words, relative to the display device or floor/ground, rows maybe horizontal, vertical or in any other orientation. Typically, however,all of the rows will be parallel to one another, as will all of thecolumns.

The depicted system may also include drive logic 306 coupled to the rowelectrodes 302 and receive logic 308 coupled to the column electrodes304. Drive logic 306 and receive logic 308 may perform a variety offunctions, and may, as in the present example, be interconnected inorder to coordinate activity, exchange data, etc. In general, drivelogic 306 is involved in causing excitation waveforms to be applied torow electrodes 302, while receive logic 308 is involved in processingand interpreting signals on column electrodes 304.

Each row electrode 302 in matrix 300 may be coupled to a respectivedriver 310 (included in drive logic 306) configured to drive itscorresponding row electrode with an excitation waveform (e.g., atime-varying voltage). In some implementations, drivers 310 of matrix300 may be driven by a micro-coded state machine implemented within afield-programmable gate array (FPGA) forming part of controller 218(FIG. 2), for example. Each driver 310 may be implemented as a shiftregister having one flip-flop and output for its corresponding rowelectrode, and may be operable to force all output values to zero,independently of register state. The inputs to each shift register maybe a clock, data input, and a blanking input, which may be driven byoutputs from the micro-coded state machine. Signals may be transmittedby filling the shift register with ones on every output to be excited,and zeroes elsewhere, and then toggling the blanking input with adesired modulation to create a transmitted waveform for exciting a rowelectrode. The excitation waveforms may be time-varying voltages that,when digitally sampled, comprise a sequence of pulses—e.g., one or moresamples of a relatively higher (or lower) digital value followed by oneor more samples of a relatively lower (or higher) digital value. If ashift register is used in this fashion, waveforms may take on only twodigital values—e.g., only binary waveforms can be transmitted. In otherimplementations, drivers 310 may be configured to transmit non-binarywaveforms that can assume three or more digital values. Non-binaryexcitation waveforms may enable a reduction in the harmonic content ofdriver output and decrease the emissions radiated by matrix 300. Instill other examples, non-quantized waveforms may play a role in rowelectrode excitation. Any practicable method may be employed by drivelogic 306 to generate appropriate excitation waveforms on the rowelectrodes 302.

In some implementations, matrix 300 may be configured to communicate andinteract with an active stylus 320 (e.g., corresponding to input device108 of FIG. 1), which may include a tip electrode 322 (also referred toas the stylus electrode or stylus tip); drive logic 324 responsible forapplying waveforms to tip electrode 322 for transmission to matrix 300;and receive logic 326 responsible for processing waveforms received frommatrix 300 (e.g., as a result of drive logic 306 exciting a rowelectrode 302 in close proximity to the stylus tip). In the context ofFIG. 1, use of a stylus such as active stylus 320 may at least partiallyenable touch sensitive display device 102 to communicate with inputdevice 108 when matrix 300 is implemented in display device 102.Specifically, an electrostatic link may be established between tipelectrode 322 and one or more row electrodes 302 or one or more columnelectrodes 304, along which data may be transmitted.

In one example, electrostatic communication is conducted viatransmission of a synchronization waveform from matrix 300 to the activestylus 320. The synchronization waveform may enable matrix 300 andstylus 322 to obtain a shared sense of time. In some examples,synchronization waveforms may be transmitted via multiple row electrodes302 simultaneously so that the active stylus can receive thesynchronization waveform regardless of the active stylus's positionrelative to the matrix. In the case that waveforms are transmitted bymultiple row electrodes 302 simultaneously, different waveforms may beused on different row electrodes 302, as explained in detail below. Insome cases, synchronization may be performed via correlation operations,in which received waveforms are processed using reference waveforms thatare based on the synchronization waveforms.

The shared sense of time may facilitate the correlation of a time atwhich the stylus detects a signal transmitted on row electrodes 302 to alocation on matrix 300. Such correlation may enable the stylus todetermine at least one coordinate (e.g., its row coordinate) relative tomatrix 300, which may be transmitted back to the matrix (e.g., via theelectrostatic link) or to an associated display via a differentcommunication protocol (e.g., radio, Bluetooth). To determine a secondcoordinate (e.g., a column coordinate) of the stylus, all row electrodes302 may be held at a constant voltage, and the stylus may transmit atime-varying voltage to matrix 300, which may measure currents resultingfrom the stylus voltage in each column electrode 304 to ascertain thesecond coordinate.

Each column electrode 304 in matrix 300 may be coupled to a respectivereceiver 312 configured to analyze received signals resulting from thetransmission of waveforms on row electrodes 302. During touch detection,matrix 300 may hold all row electrodes 302 at a constant voltage exceptfor an active row electrode 302 along which an excitation waveform istransmitted. During transmission of the excitation sequence, all columnelectrodes 304 may be held at a constant voltage (e.g., ground). Withthe excitation waveform applied to the active row electrode 302 and allcolumn electrodes 304 held at the constant voltage, a current may flowinto each of the receivers 312 as a result of application of theexcitation waveform. This current is proportional to the capacitance.Touch detection is achieved as a result of the change in capacitanceproduced, for example, by the presence of a user's finger. Matrix 300may be repeatedly scanned at a frame rate (e.g., 60 Hz, 120 Hz) topersistently detect touch input, where a complete scan of a framecomprises applying an excitation sequence to each transmit row 302, andfor each driven transmit row, collecting output from all of the receivecolumns 304. However, in other examples, a complete scan of a frame maybe a scan of a desired subset, and not all, of one or both of transmitrow electrodes 302 and receive column electrodes 304.

Higher resolution positional determinations of both a user's finger andan active stylus may be achieved via interpolation methods. Using theabove example of determining a stylus's row coordinate, measurements forrows on either side of a highest-signal row may be assessed. Assumingthe stylus detects a highest signal strength at time t(K), correspondingto the excitation of row K, the system may also take readings from anynumber or distribution of neighboring row electrodes. In onenon-limiting example, measurements are assessed for rows K−2, K−1, K+1and K+2. The distribution of received signal strength across these rowsenables the system to increase the positional resolution. Similarly,when the stylus is transmitting through operation of drive logic 324,one of the column electrodes 304 receives the strongest signal (i.e.,the nearest column to the stylus). Signal strength at nearby columns canbe used for interpolation. Similar interpolation methods may be used fordetermining finger/hand position (i.e., measure strength of signalsneighboring the highest-signal column or highest-signal row).

From the above, it will be appreciated that touch functionality (fromuser's body and stylus) occurs over an ongoing series of touch-sensingframes, during which drive logic in matrix 300 or stylus 320 driveelectrodes therein to transmit waveforms to receiving electrodes, wherethe received signals are processed by receive logic (e.g., receive logic308 or receive logic 326). FIG. 4 depicts an example touch-sensing frame400. Each touch-sensing frame 400 includes a number of differentsub-frames. One sub-frame is a stylus sync sub-frame (SSSF) 402, duringwhich, as described above, row electrodes 302 on matrix 300 transmitsynchronization waveforms to enable stylus 320 and display device 102 togain/maintain a shared sense of time.

During any given stylus sync sub-frame (SSSF) 402, the specific rowelectrodes 302 being driven with synchronization waveforms are referredto, for that stylus sync sub-frame (SSSF) 402, as sync-driven rowelectrodes. The specific sync-driven row electrodes being used may varyfrom one stylus sync sub-frame (SSSF) 402 to the next. In some cases,multiple different sets of sync-driven row electrodes may be employed,each of which omits some row electrodes 302 (e.g., two out of everythree). In other words, a given row electrode 302 may be a sync-drivenrow electrode in one set, but not in another. In some examples, a set ofsync-driven row electrodes may use differing synchronization waveforms(i.e., a waveform used on one sync-driven row electrode differs fromthat used on another in the set). Sync-driven row electrodes and thesynchronization waveforms employed with them will be discussed in moredetail below.

Two other sub-frames, also discussed above, which may be employed, are(1) a row-drive sub-frame (RDSF) 404 during which row electrodes aredriven sequentially to support determination of a row coordinate ofstylus 320 and row and column coordinates of user's body 106; and (2) astylus-drive sub-frame (SDSF) 406 during which stylus 320 is driven tofacilitate determination of its column coordinate. Touch-sensing framestypically repeat at relatively high frequencies to support rapidlyupdated touch detection with minimal lag (e.g., between finger movementand a line being drawn under the user's finger). In one example, a framerate of 120 Hz may be employed.

During the stylus sync sub-frames (SSSFs) 402, gaining and maintainingproper synchronization may depend upon whether a current havingsufficient magnitude is flowing into stylus electrode 322. Currentflowing into stylus electrode 322 may depend on various capacitancesduring the stylus sync sub-frames (SSSFs) 402. The most relevantcapacitances may be (1) Cts—capacitance from the stylus electrode 322 torow electrodes 302 being driven with synchronization waveforms; (2)Ctg—capacitance from stylus electrode 322 to a chassis ground of displaydevice 102 or equivalent (e.g., receive column electrodes 304 orinactive row electrodes 302); (3) Cbs—capacitance from the user's body106 to row electrodes 302 being driven with synchronization waveforms(i.e., sync-driven row electrodes); and (4) Cbg—capacitance from theuser's body 106 to a chassis ground of display device 102 or equivalent.

Three conditions will now be described, along with their potentialeffect upon current flowing into stylus electrode 322 in the case ofundifferentiated driving of the sync-driven row electrodes. The firstcondition may be described as:Cts/(Cts+Ctg)>>Cbs/(Cbs+Cbg)

Under these circumstances (equation 1 above), synchronization waveformson row electrodes 302 may cause sufficient current to flow into styluselectrode 322 (e.g., of sufficient SNR to derive useful synchronizationinformation from the inbound waveform).

The second condition may be described as:Cts/(Cts+Ctg)≈Cbs/(Cbs+Cbg)  (2)

Under these circumstances (equation 2 above), synchronization waveformson row electrodes 302 may cause negligible current to flow into styluselectrode 322. As a result, stylus 320 is not able to receive asufficiently strong signal to support synchronization.

The third condition may be described as:Cts/(Cts+Ctg)<<Cbs/(Cbs+Cbg)  (3)

Under these circumstances (equation 3 above), synchronization waveformson row electrodes 302 may cause current to flow out of stylus electrode322. Such reverse polarity/phase current may also hindersynchronization.

In many cases, capacitance of the user's body to driven rows of matrix300 (Cbs) will have the strongest effect on which of the above threeconditions exist during any given stylus sync sub-frame. Specifically,when the user touches display device 102 over matrix 300, Cbs increases.The increase may be substantial, particularly in the not-infrequent caseof a large contact patch (e.g., user rests their palm on the displaywhile holding the stylus). In such a case, the user's body significantlycovers sync-driven row electrodes during a series of stylus syncsub-frames (SSSFs) 402. Relative to when the stylus contacts thedisplay, the user's body overlaps more sync-driven row electrodes, andoverlaps them along a greater length. As a result of the relativelylarge increase in Cbs and the associated change at various voltagenodes, increased current may flow into the user's body, thereby reducingcurrent into the stylus electrode, in turn hindering the ability of thestylus to obtain a sufficiently strong synchronization signal.

As will now be described, the compromising of stylus current may in someexamples be improved by differentially driving sync-driven rowelectrodes in touch-sensing frames 400. In other words, within a givenstylus sync sub-frame (SSSF) 402, drive logic 306 may use onesynchronization waveform on some sync-driven row electrodes, andanother, different, synchronization waveform on other sync-driven rowelectrodes. Any number and type of different synchronization waveformsmay be used in a given stylus sync sub-frame (SSSF) 402. As described indetail below, the different synchronization waveforms are configured tocreate at least partially cancelling electrical conditions to reducecurrent flowing into a user's body that would undesirably affectsynchronization current flowing into stylus electrode 322. FIG. 5 showsan example of such differential driving. The figure shows twelve rowelectrodes 302, as driven during three successive stylus sync sub-frames(SSSFs) 402. In this example, every nth electrode (n=3 here, but couldbe any other practicable number) is a sync-driven row electrode. Onesuch sync-driven row electrode is indicated at 502 in the figure.Different sets of sync-driven row electrodes may be employed; three sets504 are depicted. In the first stylus sync sub-frame, the set ofsync-driven row electrodes (Set A) includes electrodes 001, 004, 007,010. In the figure, sync-driven row electrodes 502 are distinguishedfrom inactive row electrodes in that they are labeled with asynchronization waveform that is used on the electrode forsynchronization (waveform labels in the figure are an encircled “P” andan encircled “N,” to be explained). In Set B, the sync-driven rowelectrodes are rows 002, 005, 008, 011; in Set C, the sync-driven rowelectrodes are rows 003, 006, 009, 012. When referring to a “set” ofsync-driven row electrodes 302, or “set information,” this disclosure isreferring to the specific row electrodes that are being driven duringsync, and to the specific differential waveforms that are used for sync.In the example of FIG. 5, varied use of the three different sets causethe deployed waveforms to spatially shift in terms of row coordinatefrom frame to frame. This in turn, will cause the deployed respectivewaveforms to vary in distance to a given stylus contact point from frameto frame.

As mentioned above, different waveforms may be employed on thesync-driven row electrodes 502 in each set. Specifically, in any givenstylus sync sub-frame (SSSF) 402, drive logic 306 (FIG. 2) may beconfigured to use two or more different waveforms on differentsync-driven row electrodes for synchronization. In this example, reversepolarity waveforms are used (positive waveform indicated with anencircled “P” and negative waveform indicated with an encircled “N”). Asshown in the figure, Sets A, B and C differ from one another in that thespatial distribution of sync-driven row electrodes, inactive rowelectrodes (i.e., not driven with synchronization waveforms) andspecific synchronization waveforms are the same but shifted by one rowelectrode 302 from one set to the next. The different waveforms yield atleast partially cancelling electrical conditions (e.g., when two inversewaveforms are close to one another) to reduce current flowing into theuser's body and thereby avoid adverse impacts upon current flowing intothe stylus electrode. In all three sets, a one-by-one alternatingpolarity scheme is employed, in which every sync-driven row electrode isdriven with a synchronization waveform that is inverted with respect tothat used on the adjacent sync-driven row electrodes.

Current reduction/cancellation into the user's body may be considered interms of “spatial groupings” of sync-driven row electrodes. Referring tothe first stylus sync sub-frame (Set A), the sync-driven row electrodes502 may be grouped into various spatial groupings. One such spatialgrouping is indicated at 505, and includes two sync-driven rowelectrodes 502 (rows 004 and 007). Two-row groupings may also be formedfrom the following sync-driven row electrode pairs in Set A: 001/004 and007/010. Alternatively, a spatial grouping may include more than two rowelectrodes 302 (e.g., all four sync-driven row electrodes in Set A). Anypracticable number of sync-driven row electrodes may comprise a spatialgrouping.

When a user's body contacts display device 102, a contact patch maycover a spatial grouping of sync-driven row electrodes. Such a contactpatch is shown at 506, and sits over spatial grouping 505 so as tooverlap sync-driven row electrodes at rows 004 and 007. In many cases,the contact patch will cover a larger number of row electrodes 302; fourelectrodes, two of which are sync-driven row electrodes, are used herefor clarity. As indicated above, a contact patch with significantelectrode overlap can potentially produce a significant change incapacitance which can reduce current into a stylus tip. The oppositepolarity waveforms on electrodes 004 and 007 may produce at leastpartially cancelling electrical conditions. This can reduce the currentinto the user's body, in some cases reducing it to zero, therebyavoiding some current reduction into the stylus electrode.

It will be appreciated that these partially cancelling conditions wouldoccur in Sets A, B and C in the event of any contact patch overlappingany number of sync-driven row electrodes 302. Overlap of an even numberof electrodes potentially would allow for greater cancellation, thougheven where an odd number of sync-driven row electrodes are overlapped,sufficient cancellation may be achieved. Typically, and as in thepresent example, a plurality of spatial groupings exist across the spanof the matrix, each one including differentially driven sync-driven rowelectrodes, such that current into a user's body would be reducedrelative to that which would occur if the same waveforms were used. Insome examples, current-reducing spatial groupings may be sized based onan expected minimum size of a body contact patch. For example, thegrouping may be sized based on a patch size that would provide aparticular level of synchronization interference in the event ofundifferentiated driving of sync-driven row electrodes.

It will be appreciated that any number, type and placement of differentsynchronization waveforms may be used within a spatial grouping/contactpatch. The above example contemplates opposite polarity waveforms (e.g.,binary pulse train), alternating at every other drive electrode. Adifferent distribution might involve clustering of similar polarities(e.g., clusters of two or more positive waveforms spatially interleavedwith clusters of two or more negative waveforms). More than twodifferent waveforms may be employed. Digital waveforms taking on morethan two values may be employed. Analog waveforms may be employed.Different frequencies, phases and amplitudes may be employed. Ingeneral, any synchronization waveform configuration may be used wherethe different waveforms under a body contact patch provide somecancellation to reduce into-body current.

In certain settings, synchronization performance may be affected by thespacing between sync-driven row electrodes. For example, a higherdensity of electrodes providing cancelling waveforms may moreeffectively provide cancellation for a variety of different size contactpatches. A relatively high density would ensure, for example, that asufficient number of varied waveforms are driven underneath an expectedsmallest contact patch, i.e., sufficient to achieve a desired level ofcancellation. Additionally, a high-density scheme may decrease thenumber of sets of sync-driven row electrodes, thereby reducing thelatency for the stylus gaining the shared sense of time.

Referring to the depiction of FIG. 5, a high-density scheme potentiallycould entail all twelve row electrodes 302 being sync-driven rowelectrodes, and altering one-by-one between positive “P” synchronizationwaveform and negative “N” synchronization waveform (e.g., even rowspositive, odd rows negative). In such a case, for any given contactpoint of stylus electrode 322 on the matrix, the stylus tip would beclose enough to both waveforms that they potentially would cancel/reducecurrent flowing into the stylus, thereby weakening the receivedsynchronization signal.

Accordingly, in some cases it will be desirable to have an increaseddistance between sync-driven row electrodes, as in the every-nth exampleof FIG. 5. Therefore, when the stylus is close to a particularsync-driven row electrode, the distance to neighboring sync-driven rowelectrodes is sufficiently large so as to reduce the capacitance fromthe stylus tip to those electrodes. The stylus therefore receives astrong synchronization signal, without interference from synchronizationwaveforms on adjacent sync-driven row electrodes that would potentiallyreduce the strength of the synchronization signal.

Regardless of whether sync-driven row electrodes are closely ordistantly spaced, it may be desirable to employ different sets ofsync-driven row electrodes. When employed, the different sets may beconfigured so that, for any given point on an operative portion of atouch-sensing matrix, using at least one of the sets will cause areduction in distance, to below a threshold, between such point and aclosest sync-driven row electrode, relative to another set of thesync-driven row electrodes. For example, assuming a minimum desiredthreshold distance between a sync-driven row electrode 502 and wherestylus electrode 322 is contacting matrix 300, different sync-driven rowelectrode sets may be employed so that at least one of them includes async-driven row electrode that will be within that threshold distancefrom the stylus electrode 322, to thereby provide a sufficiently strongsignal with minimized interference from other synchronization waveforms.In other words, the different sets of sync-driven row electrodes may beconstructed such that cycling through them causes frame-to-framevariation between a stylus contact point and a closest sync-driven rowelectrode.

Referring to point 508 on the matrix (e.g., a contact point where styluselectrode 322 might contact matrix 300), it will be seen thatperformance may vary between Sets A, B and C. Cycling through the setsfrom stylus sync sub-frame to the next causes the distance between point508 and the closest sync-driven row electrodes to vary. As indicatedabove, it will normally be desirable that, for at least one of the sets,the stylus tip is relatively close to one sync-driven row electrode andrelatively distant from any sync-driven row electrode that would producecancellation (e.g., close to a one waveform and far from an inversion ofthat waveform). Referring specifically to FIG. 5, Set C provides thebest performance in this regard. In Set A and Set B, the styluselectrode would be (1) either too far from the neighboring sync-drivenrow electrodes; and/or (2) the proximity to each sync-driven rowelectrode would be sufficient, but the nearby inverted waveforms wouldreduce the signal received by the stylus.

More generally, different sets of sync-driven row electrodes, and thedifferential waveforms used to drive them, may be used to provide, for astylus electrode contact point on a matrix, varied positioning of thefollowing relative to that contact point: (1) a synchronization waveformor waveforms that cause receipt of a synchronization signal into thestylus; and (2) a synchronization waveform or waveforms that counter theeffect of (1). As indicated above, using different sets increases thepotential that the distance of (1) will be relatively small while thedistance of (2) will be relatively large.

Referring to the example of FIG. 5, drive logic 306 may selectivelyapply the different sets in any order over successive stylus syncsub-frames. In one example, the drive logic 306 cycles through themrepeatedly in the same sequence: ABCABCABC etc. In other examples, thesets are chosen randomly. In other examples, only some of the sets areused over a given period of time, with some being omitted.

In other examples, sets of sync-driven row electrodes are chosenselectively, rather than cycling through them in a predetermined order,to achieve a performance benefit. In some cases, the benefit is asdescribed above, namely placing a particular synchronization waveformclose to the stylus electrode, while ensuring that interfering waveformsare farther away. Accordingly, the drive logic 306 may select from aplurality of different sets of sync-driven row electrodes based onposition information associated with an active stylus.

Position information used for set selection may be stored in variousplaces, for example as position information 330 in drive logic 306 (FIG.3). With regard to stylus 320, position information 330 can take a widevariety of forms, including (1) current, past or predicted row andcolumn coordinates of the stylus; (2) speed of stylus movement over pasttouch-sensing frames; (3) direction of stylus movement over pasttouch-sensing frames; (4) indicators affecting the ability to predictfuture position of the stylus; etc. In general, position information caninclude any type of information that may be useful in determining wherestylus electrode 322 will be in a future touch-sensing frame. Positioninformation may be performed in any suitable manner, including via thenon-limiting examples described above, in which row drive sub-frames(RDSFs) 404 and stylus drive sub-frames (SDSFs) 406 (FIG. 4) are used toestablish row coordinates and column coordinates for stylus 320.

When predictive-quality exceeds a threshold (e.g., relatively highconfidence in future position of stylus), drive logic may enter a modewhere sync-driven row electrode sets are chosen based on the positioninformation. Referring again to the example of FIG. 5, if the system isable to predict, with sufficient accuracy, that the stylus electrodewill be very close to point 508 in an upcoming touch-sensing frame, thendrive logic 306 may employ Set C of sync-driven row electrodes forsynchronization.

The drive logic may switch into and out of position-based selection. Forexample, prior to selecting based on position, the drive logic may beoperating in a cycling mode, in which a defined sequence of sets isused, or a random cycling is used. These less-selective approaches maybe employed when the system is not able to sufficiently assess whetherone set will outperform another, in terms of its ability to effectivelyposition synchronization waveforms around the stylus electrode. Forexample, if the stylus electrode is moving quickly, beyond a velocitythreshold, then the drive logic may revert to a cycling mode (e.g., anABCABCABCABC . . . set selection from FIG. 5). In addition to or insteadof velocity thresholds, any type of threshold associated with theposition information may be used to mode switch into and out ofselecting sets of sync-driven row electrodes based on positioninformation 330.

In typical implementations, receive logic, whether in matrix 300 orstylus 320, includes specific circuitry tuned to account for theproperties of the excitation signal it receives. In some examples,receive processing is performed via correlation operations using areference signal, which typically is based off of, and in many casesidentical to, the excitation waveform. For example, if a synchronizationwaveform on a sync-driven row electrode is a 50% duty cycle square wave,a phase-aligned 50% duty cycle square wave may be used in receivecircuitry for correlation purposes (e.g., in receive logic 326 of stylus320). A high positive value in the correlation receiver indicatesaffirmative presence of the excitation signal. In the inversion examplesmentioned above (one synchronization waveform is the inversion of theother), it will often be possible to use a single receiver (i.e., onereference waveform). In more complicated examples, multiple differentreceivers may be employed, one for each different excitation waveform.

The present disclosure does contemplate examples where multipledifferent waveforms are used in a set of sync-driven row electrodes. Forexample, given a minimum expected size of a body contact patch occurringanywhere on matrix 300, a set of sync-driven row electrodes might beconstructed so that four different synchronization waveforms arepositioned underneath the contact patch. The waveforms would be designedso that they collectively at least partially cancel one another, therebyreducing current into the user's body and maintaining current intostylus electrode 322. Use of this many waveforms may provide variousbenefits, though at the expense of configuring and operating fourreceivers within receive logic 326 of stylus 320.

In some circumstances in the above example, all four receivers mustoperate simultaneously. This might occur, for example, if the stylusdoes not know its row coordinate on the matrix. Not knowing that, thestylus cannot know what the nearby synchronization waveforms will be,and thus must attempt detection on all four of the differentsynchronization waveforms. On the other hand, the stylus may know itsposition, but not have knowledge of where the different synchronizationwaveforms will be placed along the row electrodes 302 of the matrix.

Accordingly, in some examples, operation of receive logic 326 in stylus320 may be controlled based on position information (e.g., styluscoordinates) and set information for the sync-driven row electrodes(i.e., what row electrodes 302 will be activated and whatsynchronization waveforms will be used). For example, via some type ofcommunication from matrix 300 (e.g., radio or electrostatic), or throughanother method, stylus 320 may learn of the various sets of sync-drivenrow electrodes that are employed. More specifically, the stylus may knowthat a particular set will be used in a specific upcoming touch-sensingframe, and that in that set, the row electrode 302 closest to itscurrent position will be activated with a particular synchronizationwaveform. This may then enable the receive logic 326 to run only areceiver (e.g., correlation operation) particular to thatsynchronization waveform, instead of a less-targeted approach wheremultiple receivers are active. In other words, selective activation anddeactivation of receivers may be based upon knowledge of the differentsets of sync-driven row electrodes and which of such sets will bedeployed by the drive logic during an upcoming stylus sync sub-frames.

Referring now to FIG. 6, the figure depicts a touch-sensing method 600for a display device having a touch sensor with a matrix of rowelectrodes and column electrodes. The method may be employed inconnection with the systems shown in FIGS. 1-3, or withdifferently-configured systems. At 602, the method includes driving therow electrodes during a plurality of touch-sensing frames, e.g., inorder to determine row/column coordinates of a user's finger and anactive stylus. Each of the touch-sensing frames includes a stylus-syncsub-frame. At 604, the method includes driving, differentially, duringeach stylus sync sub-frame, at least some of the row electrodes,referred to for that stylus sync sub-frame as sync-driven row electrodeswith synchronization waveforms. The synchronization waveforms arecommunicated electrostatically to an active stylus to synchronize theactive stylus and the display device. The driving includesdifferentially driving the sync-driven row electrodes of the stylus syncsub-frame, such that a synchronization waveform used to drive one of thesync-driven row electrodes is different than a synchronization waveformused to drive another of the sync-driven row electrodes.

As shown at 606, the differential driving indicated at 604 may furtherinclude using two or more different synchronization waveforms to drivesync-driven row electrodes in each of a plurality of spatial groupingsof sync-driven row electrodes. The two or more different synchronizationwaveforms may be configured to produce at least partially cancellingelectrical conditions. This may reduce, in the event of a user's bodypart touching the display device on a contact patch over the spatialgrouping of sync-driven row electrodes, current flowing into the user'sbody part, relative to current which would flow in the case ofundifferentiated driving of the sync-driven row electrodes in thespatial grouping. In some examples, a spatial grouping may includesynchronization waveforms of opposite polarity to provide cancellation,though this is but one example. Any size spatial groupings may beemployed and, as described above, a wide range of different types andnumbers of waveforms may be used to achieve cancelling electricalconditions. Such cancellation may, as described above, reduce currentflowing into the user's body to avoid compromising current needed by thestylus for synchronization.

Method 600 may further include selecting from among a plurality ofdifferent sets of sync-driven row electrodes to use during stylus syncsub-frames. Typically, each set will omit some of the row electrodes ofthe matrix and will differ from the other sets (e.g., a row electrode issync-driven for one set and not for another). In some cases, the setsmay be constructed so that, for any given point on an operative portionof the matrix (i.e., a stylus contact point), using the different setscauses variation of distance between the closest sync-driven rowelectrode and the stylus contact point. Typically, one of the sets willcause a reduction in distance between the stylus contact point and aclosest sync-driven row electrode, relative to another set of thesync-driven row electrodes. The sets may be constructed so that this isbelow a threshold distance to provide desired synchronization signalstrength to the stylus. The method may also include selecting from amongthe different sets based on position information associated with theactive stylus. In one example, a set is selected to place a sync-drivenrow electrode as close as possible to the current row coordinate of thestylus, to thereby improve the strength of the synchronization signal. Avariety of other position-based selections may be employed, as describedabove with reference to FIGS. 3 and 5.

The approaches described above for increasing the strength ofelectrostatic signals transmitted to a stylus electrode may beapplicable to capacitive touch sensors other than those described above.For example, differential waveforms may be utilized in so-called“in-cell” touch sensor matrices, in addition to so-called “mutualcapacitance” touch sensor matrices, of which touch sensor matrix 300 ofFIG. 3 may be considered an example. It will be appreciated that, inFIG. 3, “matrix” refers to, among other things, the intersectionsbetween the elongate transmitting and receiving row/column electrodes,where mutual capacitance is measured at those intersections viatransmitting on one electrode and receiving on the other. In the in-celland on-cell examples below, “matrix” refers also to an array oflocations where capacitance is measured (and/or the electrodesthemselves), but the measurement locations instead are individualelectrodes (instead of electrode intersections), with self-capacitancemeasurements occurring by both transmitting and receiving at eachelectrode to establish, for example, x/y location of finger touch on thematrix. It will further be appreciated that in-cell displayimplementations are but one example setting in which the to-be-describedself-capacitance methods may be employed.

FIG. 7 shows an example touch-sensitive display device 700, including adisplay 702 and a touch sensor 704 to enable graphical output and touchinput (e.g., from a stylus or finger). Display 702 is operable to emitlight in an upward direction to yield viewable imagery at a top surface706 of the display device or other locations. Display 702 may assume theform of a liquid crystal display (LCD), organic light-emitting diodedisplay (OLED), or any other suitable display. To effect displayoperation, FIG. 7 shows display 702 coupled to a controller 708, whichmay control pixel operation, refresh rate, drive electronics, operationof a backlight if included, and/or other aspects of the display. Asuitable image source, which may be integrated with, or providedseparately from, controller 708, may provide graphical content foroutput by display 702. The image source may be a computing deviceexternal to, or integrated within, display device 700, for example.

Touch sensor 704 is operable to receive input, which may assume varioussuitable form(s). As examples, touch sensor 704 and associatedcomponentry may detect (1) touch input applied by a human digit 710 incontact with top surface 706 of display device 700; (2) a force and/orpressure applied by the human digit to the top surface; (3) hover inputassociated with a human digit near but not in contact with top surface706; (4) a height of the hovering human digit from the top surface, suchthat a substantially continuous range of heights from the top surfacecan be determined; and/or (5) input from a non-digit input device suchas an active stylus 712. As described in further detail below, touchsensor 704 may receive position, tip force, button state, and/or otherinformation from stylus 712, and in some examples may transmitinformation to the stylus. Touch sensor 704 may be operable to receiveinput from multiple input devices (e.g., digits, styluses, other inputdevices) simultaneously, in which case display device may be referred toas a “multi-touch” display device. To enable input reception, touchsensor 704 may be configured to detect changes associated with thecapacitance of a plurality of electrodes, as described in further detailbelow.

Inputs received by touch sensor 704 are operable to affect any suitableaspect of display 702 and/or a computing device operatively coupled todisplay device 700, and may include two or three-dimensional fingerinputs and/or gestures. As an example, FIG. 7 depicts the output ofgraphical content by display 702 in spatial correspondence with pathstraced out by digit 710 and stylus 712 proximate to top surface 706.While FIG. 7 shows controller 708 as effecting operation of both display702 and touch sensor 704 (e.g., electrode drive/receive operation),separate display and touch sensor controllers may be provided.

Display device 700 may be implemented in a variety of forms. Forexample, display device 700 may be implemented as a so-called“large-format” display device with a diagonal dimension of approximately1 meter or greater, or in a mobile device (e.g., tablet, smartphone)with a diagonal dimension on the order of inches. Other suitable formsare contemplated, including but not limited to desktop display monitors,high-definition television screens, tablet devices, etc.

Display device 700 may include other components in addition to display702 and touch sensor 704. As an example, FIG. 7 shows the inclusion ofan optically clear touch sheet 714 providing top surface 706 forreceiving touch input as described above. Touch sheet 714 may becomprised of any suitable materials, such as glass or plastic. Further,an optically clear adhesive (OCA) 716 bonds a bottom surface of touchsheet 714 to a top surface of display 702. As used herein, “opticallyclear adhesive” refers to a class of adhesives that transmitsubstantially all (e.g., about 99%) of incident visible light.Alternatively or additionally, display device 700 may include anysuitable components not shown in FIG. 7, including but not limited tovarious optical elements (e.g., lens, diffuser, diffractive opticalelement, waveguide, filter, polarizer).

FIG. 7 depicts the integration of touch sensor 704 within display 702 ina so-called “in-cell” touch sensor implementation. In this example, oneor more components of display device 700 may be operated to perform bothdisplay output and input sensing functions. As a particular example inwhich a display 702 is an LCD, the same physical electrode structuresmay be used both for capacitive sensing and for determining the field inthe liquid crystal material that rotates polarization to form adisplayed image. Alternative or additional components of display device700 may be employed for display and input sensing functions, however.

Other touch sensor configurations are possible. For example, touchsensor 704 may alternatively be implemented in a so-called “on-cell”configuration, in which the touch sensor is disposed directly on display702. In an example on-cell configuration, touch sensing electrodes maybe arranged on a color filter substrate of display 702. Implementationsin which touch sensor 704 is configured neither as an in-cell noron-cell sensor are possible, however. In such implementations, anoptically clear adhesive (OCA) may be interposed between display 702 andtouch sensor 704, for example.

Touch sensor 704 may be configured in various structural forms and fordifferent modes of capacitive sensing. In a self-capacitance mode, thecapacitance and/or other electrical properties (e.g., voltage, charge)between touch sensing electrodes and ground may be measured to detectinputs. In other words, properties of the electrode itself are measured,rather than in relation to another electrode in the capacitancemeasuring system. Additional detail regarding self-capacitance touchsensing is described below with reference to FIG. 8, which shows anexample self-capacitance touch sensor that can be implemented in anin-cell or on-cell fashion.

In a mutual capacitance mode, the capacitance and/or other electricalproperties between electrodes of differing electrical state may bemeasured to detect inputs. When configured for mutual capacitancesensing, and similar to the above examples, touch sensor 704 may includea plurality of vertically separated row and column electrodes that formcapacitive, plate-like nodes at row/column intersections when the touchsensor is driven. The capacitance and/or other electrical properties ofthe nodes can be measured to detect inputs.

Touch sensor 704 may include a plurality of electrodes that areconfigured to detect input in response to applied drive signals. In somecases, the drive signals are applied at the same electrode(s) at whichthe capacitance measurements are made. In other cases, the drive signalsare applied at one or more electrodes near the receiving electrode. Theelectrodes may assume a variety of suitable forms, including but notlimited to (1) elongate traces, as in row/column electrodeconfigurations, where the rows and columns are arranged at substantiallyperpendicular or oblique angles to one another; (2) substantiallycontiguous pads, as in mutual capacitance configurations in which thepads are arranged in a substantially common plane and partitioned intodrive and receive electrode sets, or as in in-cell or on-cellconfigurations; (3) meshes; and (4) an array of point electrodesarranged at specific x/y locations, as in in-cell or on-cellconfigurations.

In some scenarios, touch sensor 704 may identify the presence of aninput mechanism by driving at least a set of electrodes, and analyzingoutput resulting from such driving at the same or different set ofelectrodes. For mutual capacitance implementations, a drive signal (alsoreferred to herein as an “excitation waveform”) such as a time-varyingvoltage may be applied to a first set electrodes (e.g., “drive”electrodes), thus influencing an output signal at a second set ofelectrodes (e.g., “receive” electrodes). The presence of an inputmechanism may then be ascertained by analyzing the output signal asdescribed below.

For self-capacitance implementations, one or more electrodecharacteristics may be analyzed to identify the presence of an inputmechanism. Typically, this is implemented via driving an electrode witha drive signal, and observing the electrical behavior with receivecircuitry attached to the electrode. For example, charge accumulation atthe electrodes resulting from drive signal application can be analyzedto ascertain the presence of the input mechanism as described below. Inthese example methods, input mechanisms of the types that influencemeasurable properties of electrodes can be identified, such as humandigits, which may affect electrode conditions by providing a capacitivepath to ground for electromagnetic fields. Other methods may be used toidentify different input mechanism types, such as those with activeelectronics.

In both mutual and self-capacitance implementations, touch sensor 704may employ a correlation-based approach in analyzing output signals toperform input mechanism detection, among other potential tasks. In thisapproach, a given output signal may be correlated with one or morereference sequences using a suitable correlation operation (e.g.,cross-correlation) to obtain correlated output with a sufficientsignal-to-noise ratio. The correlation operation may yield a number thatcan be compared to a threshold such that, if the number meets or exceedsthe threshold, touch sensor 704 determines that an input mechanism ispresent, and if the number falls below the threshold, the touch sensordetermines that an input mechanism is not present. In some examples, adrive signal used to drive electrodes may form the basis for a referencesequence. Further, one or more reference sequences may be designed tomitigate noise for certain operating conditions, noise sources, and/orwavelength bands.

FIG. 8 shows an example touch sensor 800. Touch sensor 800 includes aplurality of electrodes, such as electrode 802, which are configured toreceive, via capacitance measurements, input in one or more of the formsdescribed above—e.g., touch, hover, force/pressure, and/or stylus/activeinput device. FIG. 8 is described in the context of an in-cellimplementation, in which touch sensor 800 is configured as an in-cellsensor in combination with a display as described above. As such, touchsensor 800 may be touch sensor 704 of touch-sensitive display device700, both of FIG. 7. However, touch sensor 800 may be implemented as anon-cell touch sensor, or as neither an in-cell nor on-cell sensor thatis discrete and separate from a display. For in-cell and on-cellimplementations, the plurality of electrodes is referred to herein as aplurality of “sensels”.

To enable sensel charging and the reception of resulting output, thesensels are operatively coupled to drive logic 804 and receive logic806. One or both of the drive logic and receive logic may be implementedinto a controller, such as controller 708 of FIG. 7. Via drive logic804, each sensel may be selectively driven with one or more drivesignals, and, via receive logic 806, one or more electricalcharacteristics (e.g., capacitance, voltage, charge) of the senselsinfluenced by such driving are monitored to perform input sensing. Inputsensing may also be performed at the sensels in response to drivesignals applied from an active stylus, such as active stylus 712.Receive logic 806 may perform correlation operations to perform sensing,as described above with reference to FIG. 7. In one example, output froma given sensel may be used in a correlation operation after charging ofthe sensel for an integer number of iterations in an integration period.Alternatively or additionally, the sensel may be continuously monitoredduring charging and/or discharging. In either case, self-capacitance ofthe plurality of sensels is measured for input sensing.

Due to the relatively large number of sensels included in a typicalimplementation of touch sensor 800, a limited number of sensels areshown in FIG. 8 for simplicity/clarity. Examples described belowcontemplate a particular configuration in which touch sensor 800includes 20,000 sensels—e.g., when implemented in a large-format displaydevice. Touch sensor 800 may include any suitable number of sensels,however.

In an example such as that referenced above with 20,000 sensels, thesensels may be arranged in 100 rows and 200 columns. While it may bedesirable to maximize sensing frequency by simultaneously measuringcapacitance at each sensel, this would entail provision of significantprocessing and hardware resources. In particular, 20,000 receivers(e.g., analog-to-digital converters) in receive logic 806 would beneeded to perform full-granularity, simultaneous self-capacitancemeasurements at each sensel. As such, partial-granularity, multiplexedapproaches to self-capacitance measurement may be desired to reduce thevolume of receive logic 806. Specifically, as described below, receivelogic capable of servicing only a portion of the touch sensor at onetime may be successively connected to different portions of the touchsensor over the course of a touch frame, via time multiplexing, in orderto service the entire touch sensor.

FIG. 8 illustrates one example approach to partial-granularityself-capacitance measurement in touch sensor 800. In this approach, thesensels are grouped into horizontal bands 810A-810J, each having tenrows of sensels. In this approach, self-capacitance measurements aretemporally multiplexed via a multiplexer 812, with a respectivemeasurement time slot in a touch frame being allocated for each band810. Accordingly, receive logic 806 may include a number of receiversequal to the number of sensels in a given band 810—e.g., 2,000receivers. For example, the receivers may be connected to one band in afirst time slot, then to another in the next time slot, and so on. Itwill be appreciated that the above groupings, bands, number of sensels,etc. reflect but one of many possible implementations. Different numbersof sensels may be employed; shapes and arrangements of groupings maydiffer from the depicted example; etc.

Touch sensor 800 may employ a variety of drive modes to effect senseloperation. In one drive mode, all sensels may be driven to perform inputsensing, which may simplify drive logic 804. It may be desirable toemploy such an approach even when only a portion of the touch sensor isread at any given time, as in the multiplexing scheme described above.Drive logic 804 may apply a single drive signal during a drive mode,differing drive signals during the drive mode, or may employ multipledrive modes with differing drive signals. Further, drive logic 804 mayswitch among two or more drive modes to alter input mechanism detectionand/or to facilitate communication with an active input mechanism suchas a stylus. “Drive mode” may also refer to periods in which one or moresensels are not driven but instead are receiving input from drivenelectrodes of an active stylus, as described elsewhere in more detail.

In some implementations, touch sensor 800 may be selectively operated ina “full search” mode and a “local search mode.” Full search refers tooperations, within the course of a single touch-sensing frame, thatcause the entirety of the touch sensor to be scanned for inputs. In someexamples, the touch sensor is placed into full search mode duringmultiple different intervals to scan the entire sensor. For example, inthe banded approach described above, ten different intervals could beused for full search, that is, full search mode would be employed duringten different sub-frames of the touch-sensing frame. During each fullsearch mode interval, one of the ten bands would be scanned. Stillfurther, two or more full search intervals could be allocated for eachof the ten bands, thus resulting in twenty or more full searchintervals.

Local search refers to performing an operation for only a portion of thetouch sensor in a given touch-sensing frame. In other words, for a giventouch-sensing frame, the operation is localized to a specific location(or locations) on the touch sensor, and the operation is not performedduring that frame for the remainder of the touch sensor. In one example,as will be discussed in detail below, full search mode is used to scanthe entire touch sensor for inputs, with local search being employed inthe touch-sensing frame only in a region where an active stylus isdetected (e.g., to receive electrostatic communication of pressurevalues from the stylus).

Referring again to full search, and in the context of the timemultiplexing of receive logic 806, full search mode intervals may beused successively for each band 810 in each touch-sensing frame. Thus,in each touch-sensing frame, the full search periods collectively enabledetection of finger touches and other input mechanisms, such as anactive or passive stylus, across the entire touch sensor.

In some examples, a local search period or periods may be performed toreceive stylus state information from an active stylus at touch sensor800. The stylus state information may include information regardingbattery level, firmware version, tip force/pressure values, and/orbutton state, among other potential data. In typical implementations,this local search activity also informs/confirms stylus position, sincethe strongest signals on the touch sensor will occur at the x/y styluslocation. During full search, some stylus location functionality mayalso occur—e.g., the stylus sending a locating drive signal indicating aband 810 of touch sensor 800 that corresponds to the active styluslocation. As such, the indication of a band 810 corresponding to theactive stylus location may prompt a subsequent local search in that bandto thereby receive stylus state information from the stylus andpotentially a confirmation or further pinpointing of stylus location.

Touch sensor 800 may perform multiple local searches in a single touchframe to receive stylus state information at multiple times within thetouch frame. In this way, an increased frequency of receiving stylusstate information may reduce the latency of active stylus operation.Other uses for local searching are possible. For implementations inwhich full search reveals an indeterminate location of the activestylus, such as a band 810 and not a particular x/y location, a localsearch may be performed following a rough position determination via afull search, to resolve location to a desired degree of accuracy. Thisscheme may be desirable in terms of time efficiency. Specifically, toachieve a high overall frame rate in an active stylus implementation, itmay be desirable to conduct the full search periods at a speed that doesnot allow for full resolution of stylus position. Targeted work is thendone at a specific location (local search) to pinpoint stylus location.

Referring to active stylus 814, the stylus includes electrode tip 820through which signals can be transmitted (e.g., electrostatically) toand/or received from touch sensor 800 (in combination with suitabledrive logic and a power source not shown in FIG. 8). Stylus 814 mayinclude one or more additional electrodes for various purposes, forexample to enable enhanced information about stylus position. In someexamples, stylus 814 transmits a drive signal to touch sensor 800 toenable location sensing of the stylus during full search periods.Typically, this drive signal is selected so that the receive logic 806can distinguish stylus inputs from finger inputs. In some examples, thestylus electrode drive signal is selected so that the receive logic seesan output similar to that produced by a finger, but opposite inpolarity. This can simplify the receive circuitry in some cases whilestill allowing simultaneous sensing of stylus and finger inputs.

Generally, electrostatic interaction between stylus 814 and touch sensor800 can be used to (1) determine the location of the stylus relative tothe touch sensor; (2) send/receive synchronization signals toestablish/maintain a shared sense of time between the stylus and thetouch sensor; (3) communicate state/status between the stylus anddisplay such as identifiers, stylus button state, battery level and thelike; and/or (4) transmit various other data, such as force determinedin the stylus tip, firmware updates, encryption keys/information, timeat which various events occur, etc. While not shown in FIG. 8, touchsensor 800 and stylus 814 may include components configured to enableradio communication therebetween, which may perform one or more of thefunctions described above and/or other functions.

As mentioned above, one or more synchronization periods may be employedto enable temporal synchronization between touch sensor 800 and stylus814. Any synchronization period within a touch-sensing frame shall bereferred to herein as a “stylus sync sub-frame”, and sensels driven as apart of the sync-frame are referred to herein as “sync-driven” senselsor electrodes.

To illustrate the use of full searches, local searches, andsynchronization periods, FIG. 9 shows an example touch-sensing frame 900according to which touch sensor 800 may be operated. Touch-sensing frame900 begins with a stylus synchronization sub-frame 902 in which touchsensor 800 transmits a synchronization beacon to stylus 814. However,one or more synchronization beacons maybe employed at differentlocations within the touch-sensing frame. When the stylus is in range,it receives the synchronization beacon and thereby synchronizes timingwith the display, which, due to the designed communication protocol,enables the stylus to know the exact timing of all of the sub-frames oftouch-sensing frame 900. Sync sub-frame 902 is followed by a full searchsub-frame 904A. Full search sub-frame 904A is denoted in FIG. 9 asFS(band_(A)), indicating that, while all sensels of touch sensor 800 maybe driven during the full search sub-frame, output reception and inputsensing is limited to band 810A due to the multiplexing of receive logic806 to the sensels of that band. In this example, results from the fullsearch sub-frame 904A indicate the presence/location of stylus 814 in aband 810N. As such, full search sub-frame 904A is followed by a localsearch sub-frame 906A, denoted in FIG. 9 as LS(band_(N)), indicatinglocal searching in the band 810N identified by full search sub-frame904A.

As described above, local search sub-frame 906A may be allocated forreceiving data from stylus 814, such as data relating to battery level,identification information, button state, force at electrode tip 820,and/or other stylus data described above. As local searches in generalmay be allocated for receiving stylus data beyond the approximatelylocating drive signal, it is desirable for touch sensor 800 to identifythe particular band 810 in which stylus 814 is located. To this end,stylus 814 may transmit the approximately locating drive signaldescribed above during portions of full searches (and/or potentiallyportions of local searches—e.g., during times other than those at whichstylus data beyond the drive signal is transmitted).

FIG. 9 also depicts additional full search sub-frames interspersed withlocal search sub-frames centered on the bands where the stylus is foundas a result of the full search intervals. As depicted, the intervals areas follows in sequence:

(1) a full search sub-frame 904B in band 810B;

(2) a local search sub-frame 906B at the stylus's band location;

(3) a full search sub-frame 904C in band 810C;

(4) a local search sub-frame 906C at the stylus's band location;

(5) a full search sub-frame 904D in band 810D; and

(6) a local search sub-frame 906D at the stylus's band location;

In the depicted example, the above sequence would continue through toband 810J for each touch-sensing frame 900. From the above, it will beunderstood that the band 810 multiplexed to receive logic 806 may varybetween full and local search sub-frames—e.g., the band 810 at which alocal search is performed may differ from the band investigated duringthe immediately preceding full search interval.

The execution of full searches in each of bands 810A-J may be considereda complete touch-sensing frame. Thus, in the depicted example, the fullsearch intervals identify finger touch inputs and active stylus locationover the entire panel. The local search intervals may enable otherinteraction such as communication of data from the stylus to the touchsensor/display.

Touch sensor 800 and/or stylus 814 may vary the number, inclusion,sequence, structure, duration, etc. of the various sub-frames on aframe-to-frame basis, based on operation conditions and/or otherfactors. For example, signal-to-noise conditions may influenceadjustments to the duration of various sub-frames. In another example,local search intervals may be omitted from the touch-sensing frame whenthe stylus is not present and interacting with the display, thusincreasing the frame rate for sensing finger touch. The specificapplication being controlled by touch input may influence dynamicadjustment to the configuration of the touch-sensing frame. These andother potential adjustments may be made to minimize the duration ofinput sensing and maximize frame rate to enhance performance.

As described above, a single band 810 identified by a full search may beselected for subsequent local searching. However, relatively rapid fullsearching may reduce uncertainty to a point where two or more bands mustbe searched locally. For example, local searching may additionally beperformed in one or more bands adjacent a band in which the inputmechanism location is most strongly suspected. The selection of multiplebands 810 may be desired even if the input mechanism location can besufficiently narrowed to a single band, e.g., to accommodate thepotential for rapid stylus movement over the tough sensor surface.Searching multiple bands requires additional time and it may thereforebe desirable to enhance estimations of stylus location via use of motiondata.

Specifically, in one example, location data for an input mechanism maybe updated for each frame of touch sensor 800. Historical location datamay be used to determine a stylus motion vector to future location ofthe stylus, which may or may not correspond to the location which wouldbe identified absent the motion data (i.e., using only the most recentsnapshot of stylus location). Motion prediction along these lines maypotentially limit the need to query multiple bands during local searchintervals of the touch-sensing frame.

As described above, drive logic 804 may apply a common drive signal tothe plurality of sensels. One issue potentially associated with theapplication of a common drive signal to the plurality of sensels is theinsufficient transmission of signals from touch sensor 800 to stylus814. For example, insufficient signal transmission may occur in the caseof a user being capacitively coupled to touch sensor 800 and poorlygrounded (e.g., by placing a body part in contact with a display devicein which the sensor is housed). The diminished signal transmission tostylus 814 may be worsened in some cases as the contact patch betweenthe user and display device increases. Thus, a similar issue may arisefrom the use of the common drive signal in touch sensor 800 as in touchsensor matrix 300 of FIG. 3. Synchronization in particular may beaffected when insufficient current flows into the stylus tip electrode820.

To address the issues described above in connection with the use of acommon, undifferentiated, drive signal, drive logic 804 may applydifferential excitation waveforms to at least a set of the sensels. Tothis end, FIG. 10 shows an example sensel grouping 1000 that may beimplemented in touch sensor 800. In grouping 1000, the sensels arearranged in rectangular sets that alternate with respect to excitationwaveforms in both the row and column directions. For example, a firstexcitation waveform (represented by diagonal shading) is applied to afirst set 1002A, whereas a second excitation waveform (represented by alack of shading) is applied to a second set 1002B and a third set 1002C,which are adjacent to the first set in the row and column directions,respectively. Grouping 1000, and the other groupings shown in FIGS. 10and 11, generally represent example spatial arrangements of sensels thatmay be employed with the use of differential waveforms in an in-celltouch sensor. The sensel sets included in a spatial sensel grouping mayinclude any suitable number of individual sensels—e.g., a single sensel;two or more sensels; tens, hundreds, or thousands of sensels; allsensels within a given column section of a band 810, such that thenumber of rows within the sensel set is equal to the number of senselrows in that band. With reference to touch sensor 800, the sensel setsshown in FIGS. 10 and 11 may cover the entire touch sensor, or in otherexamples may cover merely a portion of the touch sensor, in which casethe sets and/or groupings may be at least partially repeated. Senselnumbers in a given sensel set may be equal or unequal in the row andcolumn directions, and set numbers in a given spatial grouping may beequal or unequal. Rectangular, Euclidean, non-Euclidean, and/or othergeometries may be employed in arranging sensels, sensel sets, andspatial groupings of sensels. Further, sensel sets and/or spatialgroupings of sensel sets may be chosen as a function of an expectedcontact patch (e.g., minimum size) of an input mechanism, such as thecontact patch of a human digit or heel of a human palm.

As additional examples, FIG. 10 shows spatial groupings 1004 and 1006.In spatial grouping 1004, the first excitation waveform is applied to afirst set 1004A, and the second excitation waveform is applied to asecond set 1004B adjacent to the first set in the column direction. Inspatial grouping 1006, the first excitation waveform is applied to afirst set 1006A, and the second excitation waveform is applied to asecond set 1006B adjacent to the first set in the row direction. It willbe understood that the designation between “row” and “column” isarbitrary in that the row and column directions described herein can bereversed, such that the row direction (e.g., horizontal direction)becomes the column direction (e.g., vertical direction) and the columndirection becomes the row direction. In the sensel groupings shown inFIGS. 10 and 11, for example, the row/column directions can be reversedsuch that the spatial alternation between waveforms also reverses withrespect to the row/column directions.

The first and second excitation waveforms may assume any suitable form.In some examples, the first excitation waveform may be a substantialinverse of the second excitation waveform to enable at least partialcancellation of current flowing into a user's body, as described above.Further, three or more excitation waveforms, at least partiallycancelling each other and/or to varying degrees, may be employed withthe groupings shown in FIGS. 10 and 11. Still further, the excitationwaveform applied to a given grouping may be alternated over time.Generally, the groupings described herein may be configured or modifiedto support any suitable set of excitation waveforms, which may includeany suitable number, type, and/or spatial arrangement of waveformsacross the sensels. In this way, the current flowing into a user's bodypart capacitively coupled to touch sensor 800 may be reduced as comparedto non-differential driving schemes, thus ensuring desired current flowinto stylus electrode(s).

As another example, FIG. 11 shows an example sensel grouping 1100 thatmay be implemented in touch sensor 800. In grouping 1100, the senselsare arranged in rectangular sets that alternate with respect toexcitation waveforms in successive sets of four in the row direction,and alternate back-to-back in the column direction. For example, a firstexcitation waveform (represented by diagonal shading) is applied to asuccessive set of four sets 1102A-D, whereas a second excitationwaveform (represented by a lack of shading) is applied to a successiveset of four sets 1104A-D following the four sets 1102A-D in the rowdirection. The second excitation waveform is applied to a set 1106Aadjacent to the set 1102A. As described above with reference to FIG. 10,the first and second excitation waveforms may be substantial inverses,and in some examples three or more excitation waveforms may be employedwith grouping 1100. Further, the excitation waveform applied to one ormore sets in grouping 1100 may be alternated over time (e.g.,frame-to-frame to provide varying performance at a given location, asdiscussed with reference to FIG. 5). Generally, grouping 1100 may beconfigured or modified to support any suitable set of excitationwaveforms, which may include any suitable number, type, and/or spatialarrangement of waveforms across the sensels. In this way, the currentflowing into a user's body part capacitively coupled to touch sensor 800may be reduced as compared to non-differential driving schemes, suchthat desired current flow into stylus electrode(s) is enabled. FIG. 11also shows the application of spatial groupings 1000, 1004, and 1006relative to the differential driving scheme shown therein.

Attributes of groupings may be varied over time, including but notlimited to grouping number, sensel number, and grouping geometry, asdescribed above. In some examples, a set of sensels, and not all of thesensels of a touch sensor, may be driven at any given time. The set ofdriven sensels may be varied over time. Further, the approachesdescribed above for reducing the attenuation of capacitive communicationbetween a stylus and in-cell touch sensor may be applied to any suitabletype of signal transmission, including stylus synchronization signals aswell as non-synchronization signals. Generally, differential driving ofan in-cell touch sensor may be employed during scenarios in whichcapacitive communication with a stylus may be adversely affected by thepresence of a user's body.

Drive logic 804 may be configured to enable the selected groupingapplied to touch sensor 800. For example, the sensels in each spatialgrouping set may be commonly coupled to drive logic 804 and isolatedfrom other sets to enable the selective driving of each set in thespatial groupings. Similarly common couplings may be employed to achieveother groupings. In yet other examples, one or more (e.g., all) of thesensels may be individually coupled to drive logic 804 to enable eachsensel to be uniquely and selectively driven, which may afford greaterflexibility in the selection of sensel groupings. In some examples inwhich partial-granularity self-capacitance measurement is employed asdescribed above, the number of rows in each grouping set may be equal tothe number of rows in each horizontal band.

Drive logic 804 may select a spatial grouping to achieve a distancebetween the location of stylus 814 and a closest driven sensel that isbelow a threshold distance. For example, assuming a minimum desiredthreshold distance between a driven sensel and stylus 814 contact pointon touch sensor 800, different spatial groupings may be employed so thatat least one grouping includes a driven sensel (or sensel set) that iswithin the threshold distance from the stylus contact point, to therebyprovide a sufficiently strong signal with minimized interference fromother waveforms. In other words, the different spatial groupings may beconstructed such that cycling through the groupings causesframe-to-frame variation between a stylus contact point and a closestdriven sensel. Further, drive logic 804 may select a spatial grouping,sensel set, or any other hierarchical arrangement of sensels foralternative or additional purposes (e.g., to minimize signalattenuation, increase SNR of stylus communication, increase SNR ofsensing, reduce power consumption). In some examples, stylus 814 mayinclude receive logic configured to selectively activate and deactivatemultiple different receivers within the receive logic based on knowledgeof differential synchronization forms to be deployed by drive logic 814during an upcoming stylus sync sub-frame. For example, the stylusreceive logic may have knowledge of one or more of a spatial grouping ofsensels, sensel set, or other hierarchical arrangement of sensels to beused by touch sensor 800.

The following example spatial sensel groupings are further contemplated:(1) a grouping alternating between first and second excitation waveformsin the diagonal direction, (2) successive sets of five (or any othersuitable integer number) sensel sets alternating between first andsecond excitation waveforms in the row direction, (3) sets thatalternate in one of the row/column directions and not in the other ofthe row/column directions, (4) sets that alternate in some regions oftouch sensor 800 but not in others, and (5) sets in which only some, andnot all, of the sensels in the set are differentially driven (e.g., thenon-differentially driven sensels are not driven).

FIG. 12 shows a flowchart illustrating an example touch-sensing method1200 for a display device having a touch sensor with a plurality ofelectrodes. The plurality of electrodes may be a plurality of sensels.Method 1200 may be executed on touch sensor 800 of FIG. 8, for example.

At 1202, method 1200 includes driving the plurality of electrodes duringa plurality of touch-sensing frames, e.g., in order to determine x/ycoordinates of a user's finger and an active stylus. Each of thetouch-sensing frames includes a stylus-sync sub-frame. At 1204, method1200 includes driving, differentially, during each stylus syncsub-frame, at least some of the plurality of electrodes, referred to forthat stylus sync sub-frame as sync-driven electrodes withsynchronization waveforms. The synchronization waveforms arecommunicated electrostatically to an active stylus to synchronize theactive stylus and the touch sensor. The driving includes differentiallydriving the sync-driven electrodes of the stylus sync sub-frame, suchthat a synchronization waveform used to drive one of the sync-drivenelectrodes is different than a synchronization waveform used to driveanother of the sync-driven electrodes.

As shown at 1206, the differential driving indicated at 1204 may furtherinclude using two or more different synchronization waveforms to drivesync-driven electrodes in each of a plurality of spatial groupings ofsensels. The two or more different synchronization waveforms may beconfigured to produce at least partially cancelling electricalconditions. This may reduce, in the event of a user's body part touchingthe display device on a contact patch over the spatial grouping ofsync-driven electrodes, current flowing into the user's body part,relative to current which would flow in the case of undifferentiateddriving of the sync-driven electrodes in the spatial grouping. In someexamples, a spatial grouping may include synchronization waveforms ofopposite polarity to provide cancellation, though this is but oneexample. Any size spatial groupings may be employed and, as describedabove, a wide range of different types and numbers of waveforms may beused to achieve cancelling electrical conditions. Such cancellation may,as described above, reduce current flowing into the user's body to avoidcompromising current needed by the stylus for synchronization.

Method 1200 may further include selecting from among a plurality ofdifferent sets of sync-driven electrodes to use during stylus syncsub-frames. Typically, each set will omit some of the electrodes of thetouch sensor and will differ from the other sets (e.g., an electrode issync-driven for one set and not for another). In some cases, the setsmay be constructed so that, for any given point on an operative portionof the touch sensor (i.e., a stylus contact point), using the differentsets causes variation of distance between the closest sync-drivenelectrode and the stylus contact point. Typically, one of the sets willcause a reduction in distance between the stylus contact point and aclosest sync-driven electrode, relative to another set of thesync-driven electrodes. The sets may be constructed so that this isbelow a threshold distance to provide desired synchronization signalstrength to the stylus. The method may also include selecting from amongthe different sets based on position information associated with theactive stylus. In one example, a set is selected to place a sync-drivenelectrode as close as possible to the current y-coordinate of thestylus, to thereby improve the strength of the synchronization signal. Avariety of other position-based selections may be employed.

FIG. 13 schematically shows a non-limiting embodiment of a computingsystem 1300, one or more aspects of which may be used to implement thetouch-sensing systems and methods described above. Computing system 1300is shown in simplified form. Computing system 1300 may take the form ofone or more personal computers, server computers, tablet computers,home-entertainment computers, network computing devices, gaming devices,mobile computing devices, mobile communication devices (e.g., smartphone), wearable devices, and/or other computing devices.

Computing system 1300 includes a logic machine 1302 and a storagemachine 1304. Computing system 1300 may optionally include a displaysubsystem 1306, input subsystem 1308, communication subsystem 1310,and/or other components not shown in FIG. 13.

Logic machine 1302 may include one or more physical devices configuredto execute instructions. For example, the logic machine may beconfigured to execute instructions that are part of one or moreapplications, services, programs, routines, libraries, objects,components, data structures, or other logical constructs. Suchinstructions may be implemented to perform a task, implement a datatype, transform the state of one or more components, achieve a technicaleffect, or otherwise arrive at a desired result.

The logic machine may include one or more processors configured toexecute software instructions. Additionally or alternatively, the logicmachine may include one or more hardware or firmware logic machinesconfigured to execute hardware or firmware instructions. Processors ofthe logic machine may be single-core or multi-core, and the instructionsexecuted thereon may be configured for sequential, parallel, and/ordistributed processing. Individual components of the logic machineoptionally may be distributed among two or more separate devices, whichmay be remotely located and/or configured for coordinated processing.Aspects of the logic machine may be virtualized and executed by remotelyaccessible, networked computing devices configured in a cloud-computingconfiguration.

The logic machine may correspond to one or more of the various drivelogic and receive logic described above. For example, logic andassociated instructions may be implemented to select and apply waveformsto drive electrodes to achieve synchronization; process inbound signalsinduced as a result of excitation of capacitively coupled electrodes;determine position of an active stylus; select from different sets ofsync-driven electrodes; etc.

Storage machine 1304 includes one or more physical devices configured tohold instructions executable by the logic machine to implement themethods and processes described herein. When such methods and processesare implemented, the state of storage machine 1304 may betransformed—e.g., to hold different data.

Storage machine 1304 may include removable and/or built-in devices.Storage machine 1304 may include optical memory (e.g., CD, DVD, HD-DVD,Blu-Ray Disc, etc.), semiconductor memory (e.g., RAM, EPROM, EEPROM,etc.), and/or magnetic memory (e.g., hard-disk drive, floppy-disk drive,tape drive, MRAM, etc.), among others. Storage machine 1304 may includevolatile, nonvolatile, dynamic, static, read/write, read-only,random-access, sequential-access, location-addressable,file-addressable, and/or content-addressable devices.

Storage machine 1304 includes one or more physical devices. However,aspects of the instructions described herein alternatively may bepropagated by a communication medium (e.g., an electromagnetic signal,an optical signal, etc.) that is not held by a physical device for afinite duration.

Aspects of logic machine 1302 and storage machine 1304 may be integratedtogether into one or more hardware-logic components. Such hardware-logiccomponents may include field-programmable gate arrays (FPGAs), program-and application-specific integrated circuits (PASIC/ASICs), program- andapplication-specific standard products (PSSP/ASSPs), system-on-a-chip(SOC), and complex programmable logic devices (CPLDs), for example.

The terms “module,” “program,” and “engine” may be used to describe anaspect of computing system 1300 implemented to perform a particularfunction. In some cases, a module, program, or engine may beinstantiated via logic machine 1302 executing instructions held bystorage machine 1304. It will be understood that different modules,programs, and/or engines may be instantiated from the same application,service, code block, object, library, routine, API, function, etc.Likewise, the same module, program, and/or engine may be instantiated bydifferent applications, services, code blocks, objects, routines, APIs,functions, etc. The terms “module,” “program,” and “engine” mayencompass individual or groups of executable files, data files,libraries, drivers, scripts, database records, etc.

A “service”, as used herein, is an application program executable acrossmultiple user sessions. A service may be available to one or more systemcomponents, programs, and/or other services. In some implementations, aservice may run on one or more server-computing devices.

When included, display subsystem 1306 may be used to present a visualrepresentation of data held by storage machine 1304. This visualrepresentation may take the form of a graphical user interface (GUI). Asthe herein described methods and processes change the data held by thestorage machine, and thus transform the state of the storage machine,the state of display subsystem 1306 may likewise be transformed tovisually represent changes in the underlying data. Display subsystem1306 may include one or more display devices utilizing virtually anytype of technology. Such display devices may be combined with logicmachine 1302 and/or storage machine 1304 in a shared enclosure, or suchdisplay devices may be peripheral display devices.

When included, input subsystem 1308 may comprise or interface with oneor more user-input devices such as a keyboard, mouse, touch screen, orgame controller. In some embodiments, the input subsystem may compriseor interface with selected natural user input (NUI) componentry. Suchcomponentry may be integrated or peripheral, and the transduction and/orprocessing of input actions may be handled on- or off-board. Example NUIcomponentry may include a microphone for speech and/or voicerecognition; an infrared, color, stereoscopic, and/or depth camera formachine vision and/or gesture recognition; a head tracker, eye tracker,accelerometer, and/or gyroscope for motion detection and/or intentrecognition; as well as electric-field sensing componentry for assessingbrain activity.

When included, communication subsystem 1310 may be configured tocommunicatively couple computing system 1300 with one or more othercomputing devices. Communication subsystem 1310 may include wired and/orwireless communication devices compatible with one or more differentcommunication protocols. As non-limiting examples, the communicationsubsystem may be configured for communication via a wireless telephonenetwork, or a wired or wireless local- or wide-area network. In someembodiments, the communication subsystem may allow computing system 1300to send and/or receive messages to and/or from other devices via anetwork such as the Internet.

Another example provides a touch sensing system comprising a displaydevice including a touch sensor having a plurality of electrodes, anddrive logic coupled to the plurality of electrodes and configured todrive the plurality of electrodes during a plurality of touch-sensingframes, each of which includes a stylus sync sub-frame during which thedrive logic drives at least some of the plurality of electrodes,referred to for that stylus sync sub-frame as sync-driven electrodes,with synchronization waveforms that are communicated electrostaticallyto cause synchronization of the display device with an active stylus,where for each of the stylus sync sub-frames, the drive logic isconfigured to differentially drive the sync-driven electrodes of suchstylus sync sub-frame, such that a first synchronization waveform usedto drive one of the sync-driven electrodes is different than a secondsynchronization waveform used to drive another of the sync-drivenelectrodes. In such an example, the drive logic may be configured to,for each stylus sync sub-frame, differentially drive sync-drivenelectrodes during that sub-frame such that, for a plurality of spatialgroupings of sync-driven electrodes, two or more differentsynchronization waveforms are used to drive the sync-driven electrodesin the spatial grouping, the two or more different synchronizationwaveforms being configured to produce at least partially cancellingelectrical conditions to reduce, in the event of a user's body parttouching the display device on a contact patch over the spatial groupingof sync-driven electrodes, current flowing into the user's body part,relative to current which would flow in the case of undifferentiateddriving of the sync-driven electrodes in the spatial grouping. In suchan example, the drive logic may be configured, for any given one of thestylus sync sub-frames, to select from among a plurality of sets ofsync-driven electrodes and differentially drive sync-driven electrodesin that set of sync-driven electrodes during the stylus sync sub-frame.In such an example, the spatial groupings may be distributed over aplurality of electrode sets that alternate in a row direction and in acolumn direction with respect to the two or more differentsynchronization waveforms. In such an example, the electrode sets thatalternate in the column direction may be longer than the electrode setsthat alternate in the row direction. In such an example, the drive logicmay switch into and out of position-based selection of the plurality ofspatial groupings of sync-driven electrodes. In such an example, thetouch-sensing system alternatively or additionally may comprise anactive stylus having receive logic configured to selectively activateand deactivate multiple different receivers within the receive logicbased on knowledge of differential synchronization forms to be deployedby the drive logic during an upcoming stylus sync sub-frame. In such anexample, within each spatial grouping, the drive logic may drivesync-driven electrodes using synchronization waveforms of oppositepolarity. In such an example, the spatial groupings may be sized basedon an expected minimum size of the contact patch. In such an example,the touch sensor may be an in-cell touch sensor.

Another example provides a touch-sensing method for a display devicehaving a touch sensor with a matrix of electrodes comprising driving theelectrodes during a plurality of touch-sensing frames, each of whichincludes a stylus sync sub-frame, and during each stylus sync sub-frame,driving at least some of the electrodes, referred to for that stylussync sub-frame as sync-driven electrodes, with synchronization waveformsconfigured to be electrostatically communicated to an active stylus tosynchronize the display device and the active stylus, where such drivingduring each stylus sync sub-frame includes differentially driving thesync-driven electrodes of that stylus sync sub-frame, such that a firstsynchronization waveform used to drive one of the sync-driven electrodesis different than a second synchronization waveform used to driveanother of the sync-driven electrodes. In such an example, for eachstylus sync sub-frame, differentially driving the sync-driven electrodesin that stylus sync sub-frame may include, for each of a plurality ofspatial groupings of sync-driven electrodes in that stylus syncsub-frame, using two or more different synchronization waveforms todrive the sync-driven electrodes in the spatial grouping, the two ormore different synchronization waveforms being configured to produce atleast partially cancelling electrical conditions to reduce, in the eventof a user's body part touching the display device on a contact patchover the spatial grouping of sync-driven electrodes, current flowinginto the user's body part, relative to current which would flow in thecase of undifferentiated driving of the sync-driven electrodes in thespatial grouping. In such an example, synchronization waveforms ofopposite polarity may be used on sync-driven electrodes within each ofthe spatial groupings. In such an example, the differential driving ofthe sync-driven electrodes during each of the stylus sync sub-frame mayinclude, for any given stylus sync sub-frame, selecting from among aplurality of sets of sync-driven electrodes and differentially drivingthe sync-driven electrodes in that set during the stylus sync sub-frame.In such an example, the spatial groupings may be distributed over aplurality of electrode sets that alternate in a row direction and in acolumn direction with respect to the two or more differentsynchronization waveforms. In such an example, the electrode sets thatalternate in the column direction may be longer than the electrode setsthat alternate in the column direction.

Another example provides a touch-sensing system comprising a displaydevice including a touch sensor having a matrix of electrodes, drivelogic coupled to the electrodes, where the drive logic is configured todrive the electrodes during a plurality of touch-sensing frames, each ofwhich includes a stylus sync sub-frame during which the drive logicdrives at least some of the electrodes, referred to for that stylus syncsub-frame as sync-driven electrodes, with synchronization waveforms tofacilitate synchronization of the display device with an active stylus,where the drive logic is configured, for any given one of the stylussync sub-frames, to select from among a plurality of sets of sync-drivenelectrodes and differentially drive sync-driven electrodes in that setof sync-driven electrodes during the stylus sync sub-frame, and wherefor each of the sets of sync-driven electrodes, the differential drivingincludes, for each a plurality of spatial groupings of sync-drivenelectrodes in the set, using two or more different synchronizationwaveforms in the spatial grouping which are configured to produce atleast partially cancelling electrical conditions to reduce, in the eventof a user's body part touching the display device on a contact patchover the spatial grouping, current flowing into the user's body part,relative to current which would flow in the case of undifferentiateddriving of the sync-driven electrodes in the spatial grouping. In suchan example, within each spatial grouping, the drive logic may drivesync-driven electrodes using synchronization waveforms of oppositepolarity. In such an example, the electrode sets that alternate in thecolumn direction may be longer than the electrode sets that alternate inthe row direction. In such an example, the spatial groupings may bedistributed over a plurality of electrode sets that alternate in a rowdirection and in a column direction with respect to the two or moredifferent synchronization waveforms.

The configurations and/or approaches described herein are exemplary innature, and that these specific embodiments or examples are not to beconsidered in a limiting sense, because numerous variations arepossible. The specific routines or methods described herein mayrepresent one or more of any number of processing strategies. As such,various acts illustrated and/or described may be performed in thesequence illustrated and/or described, in other sequences, in parallel,or omitted. Likewise, the order of the above-described processes may bechanged.

The subject matter of the present disclosure includes all novel andnonobvious combinations and subcombinations of the various processes,systems and configurations, and other features, functions, acts, and/orproperties disclosed herein, as well as any and all equivalents thereof.

The invention claimed is:
 1. A touch sensing system, comprising: adisplay device including a touch sensor having a plurality ofelectrodes; and drive logic coupled to the plurality of electrodes andconfigured to drive the plurality of electrodes during a plurality oftouch-sensing frames, each of which includes a stylus sync sub-frameduring which the drive logic drives at least some of the plurality ofelectrodes, referred to for that stylus sync sub-frame as sync-drivenelectrodes, with synchronization waveforms that are communicatedelectrostatically to cause synchronization of the display device with anactive stylus; where for each of the stylus sync sub-frames, the drivelogic is configured to differentially drive the sync-driven electrodesof such stylus sync sub-frame, such that a first synchronizationwaveform used to drive one of the sync-driven electrodes is differentthan a second synchronization waveform used to drive another of thesync-driven electrodes.
 2. The touch-sensing system of claim 1, wherethe drive logic is configured to, for each stylus sync sub-frame,differentially drive sync-driven electrodes during that sub-frame suchthat, for a plurality of spatial groupings of sync-driven electrodes,two or more different synchronization waveforms are used to drive thesync-driven electrodes in the spatial grouping, the two or moredifferent synchronization waveforms being configured to produce at leastpartially cancelling electrical conditions to reduce, in the event of auser's body part touching the display device on a contact patch over thespatial grouping of sync-driven electrodes, current flowing into theuser's body part, relative to current which would flow in the case ofundifferentiated driving of the sync-driven electrodes in the spatialgrouping.
 3. The touch-sensing system of claim 2, where the spatialgroupings are distributed over a plurality of electrode sets thatalternate in a row direction and in a column direction with respect tothe two or more different synchronization waveforms.
 4. Thetouch-sensing system of claim 3, where the electrode sets that alternatein the column direction are longer than the electrode sets thatalternate in the row direction.
 5. The touch-sensing system of claim 2,where: the drive logic is configured, for any given one of the stylussync sub-frames, to select from among a plurality of sets of sync-drivenelectrodes and differentially drive sync-driven electrodes in that setof sync-driven electrodes during the stylus sync sub-frame.
 6. Thetouch-sensing system of claim 2, where the drive logic switches into andout of position-based selection of the plurality of spatial groupings ofsync-driven electrodes.
 7. The touch-sensing system of claim 2, furthercomprising an active stylus having receive logic configured toselectively activate and deactivate multiple different receivers withinthe receive logic based on knowledge of differential synchronizationforms to be deployed by the drive logic during an upcoming stylus syncsub-frame.
 8. The touch-sensing system of claim 2, where within eachspatial grouping, the drive logic drives sync-driven electrodes usingsynchronization waveforms of opposite polarity.
 9. The touch-sensingsystem of claim 2, where the spatial groupings are sized based on anexpected minimum size of the contact patch.
 10. The touch-sensing systemof claim 1, where the touch sensor is an in-cell touch sensor.
 11. Atouch-sensing method for a display device having a touch sensor with amatrix of electrodes, comprising: driving the electrodes during aplurality of touch-sensing frames, each of which includes a stylus syncsub-frame; and during each stylus sync sub-frame, driving at least someof the electrodes, referred to for that stylus sync sub-frame assync-driven electrodes, with synchronization waveforms configured to beelectrostatically communicated to an active stylus to synchronize thedisplay device and the active stylus, where such driving during eachstylus sync sub-frame includes differentially driving the sync-drivenelectrodes of that stylus sync sub-frame, such that a firstsynchronization waveform used to drive one of the sync-driven electrodesis different than a second synchronization waveform used to driveanother of the sync-driven electrodes.
 12. The touch-sensing method ofclaim 11, where for each stylus sync sub-frame, differentially drivingthe sync-driven electrodes in that stylus sync sub-frame includes, foreach of a plurality of spatial groupings of sync-driven electrodes inthat stylus sync sub-frame, using two or more different synchronizationwaveforms to drive the sync-driven electrodes in the spatial grouping,the two or more different synchronization waveforms being configured toproduce at least partially cancelling electrical conditions to reduce,in the event of a user's body part touching the display device on acontact patch over the spatial grouping of sync-driven electrodes,current flowing into the user's body part, relative to current whichwould flow in the case of undifferentiated driving of the sync-drivenelectrodes in the spatial grouping.
 13. The touch-sensing method ofclaim 12, where synchronization waveforms of opposite polarity are usedon sync-driven electrodes within each of the spatial groupings.
 14. Thetouch-sensing method of claim 12, where the differential driving of thesync-driven electrodes during each of the stylus sync sub-frameincludes, for any given stylus sync sub-frame, selecting from among aplurality of sets of sync-driven electrodes and differentially drivingthe sync-driven electrodes in that set during the stylus sync sub-frame.15. The touch-sensing method of claim 12, where the spatial groupingsare distributed over a plurality of electrode sets that alternate in arow direction and in a column direction with respect to the two or moredifferent synchronization waveforms.
 16. The touch-sensing method ofclaim 12, where the electrode sets that alternate in the columndirection are longer than the electrode sets that alternate in thecolumn direction.
 17. A touch-sensing system, comprising: a displaydevice including a touch sensor having a matrix of electrodes; drivelogic coupled to the electrodes; where the drive logic is configured todrive the electrodes during a plurality of touch-sensing frames, each ofwhich includes a stylus sync sub-frame during which the drive logicdrives at least some of the electrodes, referred to for that stylus syncsub-frame as sync-driven electrodes, with synchronization waveforms tofacilitate synchronization of the display device with an active stylus;where the drive logic is configured, for any given one of the stylussync sub-frames, to select from among a plurality of sets of sync-drivenelectrodes and differentially drive sync-driven electrodes in that setof sync-driven electrodes during the stylus sync sub-frame; and wherefor each of the sets of sync-driven electrodes, the differential drivingincludes, for each a plurality of spatial groupings of sync-drivenelectrodes in the set, using two or more different synchronizationwaveforms in the spatial grouping which are configured to produce atleast partially cancelling electrical conditions to reduce, in the eventof a user's body part touching the display device on a contact patchover the spatial grouping, current flowing into the user's body part,relative to current which would flow in the case of undifferentiateddriving of the sync-driven electrodes in the spatial grouping.
 18. Thetouch-sensing system of claim 17, where within each spatial grouping,the drive logic drives sync-driven electrodes using synchronizationwaveforms of opposite polarity.
 19. The touch-sensing system of claim17, where the electrode sets that alternate in the column direction arelonger than the electrode sets that alternate in the row direction. 20.The touch-sensing system of claim 17, where the spatial groupings aredistributed over a plurality of electrode sets that alternate in a rowdirection and in a column direction with respect to the two or moredifferent synchronization waveforms.